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Nitric oxide synthase is a cytochrome P-450 type hemoprotein
1Department of Biological Chemistry, Medical School, University of Michigan, Ann Arbor 48109-1065.
Biochemistry
|July 28, 1992
Summary
Nitric oxide synthase (NOS) is identified as a cytochrome P-450 hemoprotein, a novel finding in soluble eukaryotic enzymes. This discovery reveals NOS
Area of Science:
- Biochemistry
- Enzymology
- Molecular Biology
Background:
- Nitric oxide (NO) is a crucial mammalian metabolic intermediate.
- NO plays vital roles in vasodilation, neuronal transmission, and cytostasis.
- Nitric oxide synthase (NOS) synthesizes NO from L-arginine.
Purpose of the Study:
- To identify the inducible macrophage nitric oxide synthase (iNOS).
- To characterize the enzymatic properties of iNOS.
- To determine the role of heme in NOS function.
Main Methods:
- Pyridine hemochrome assay to detect heme presence.
- Carbon monoxide (CO) binding spectrum analysis.
- Enzyme inhibition studies using CO/O2 mixtures.
Main Results:
- Inducible macrophage NOS identified as a cytochrome P-450 type hemoprotein.
- NOS contains a bound protoporphyrin IX heme, with CO binding at 447 nm.
- CO/O2 mixture significantly inhibited NOS activity, confirming heme's role in catalysis.
- NOS is the first soluble eukaryotic cytochrome P-450 and a self-sufficient mammalian P-450 enzyme.
Conclusions:
- The inducible macrophage NOS is a cytochrome P-450 hemoprotein.
- The heme group is essential for the catalytic activity of NOS.
- NOS represents a unique class of soluble, self-sufficient P-450 enzymes in mammals.
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